Prostaglandin D2 (PGD2) is synthesized in a number of tissues including brain, spleen, lung, mast cells, bone marrow, stomach, skin and eye (Negishi M., et al., Prog. Lipid Res. 32:417-434, 1993, and references within). Central nervous system actions of PGD2 are thought to involve effects on sleep induction, body temperature, olfactory function, hormone release, inflammation and analgesia (Negishi M., et al., supra, and references within). PGD2 can cause inhibition of platelet aggregation (Coleman R. A., et al., Pharmacological Reviews 46:205-229, 1994, and references within). PGD2 is also the predominant prostanoid released from mast cells upon immunologic challenge and as such is thought to be a mediator of various allergic disorders including but not limited to allergic rhinitis and airway hyperreactivity (Ito S. et al., Prostaglandins Leukotrienes and Essential Fatty Acids. 37:219-234, 1989, and references within). It may also stimulate secretion in the intestine. Topically applied PGD2 has also been shown to reduce intraoccular pressure (Woodward D. F., et al. European J. Pharmacology. 230:327-333, 1993, and Nakajima M., et al., Graefe""s Arch. Clin. Exp. Ophthalmol. 229:411-413, 1991).
The physiological actions of PGD2 are mediated through interaction with the prostanoid DP receptor. The DP receptors are thought to be distributed mainly in blood platelets, smooth muscle of various tissues and nervous tissue, including the central nervous system (Coleman R. A., et al., supra, and references within). However, the DP receptor is the least ubiquitous and least abundant of the prostanoid receptors and as such is the one least well characterized. To further complicate matters many of the actions of PGD2 and distribution of their receptor are also species dependent. Specific binding sites for the DP receptor have been tentatively studied using human platelet membranes, rat brain synaptic membranes and membranes prepared from a cell line derived from bovine embryonic trachea (Coleman R. A., et al., supra, and references within).
The above methods for studying DP receptor activities have several disadvantages in that most if not all preparations contain several different but related prostanoid receptor populations, each with different ligand binding properties, making measurements of absolute potency and selectivity very unpredictable. In addition, the low abundance of the DP receptor in various tissues or cells makes it very difficult to satisfactorily test for compounds as modulators, effectors, agonists or antagonists, of the human DP receptor.
A novel prostaglandin receptor protein termed DP has been identified from human cells. A DNA molecule encoding the full length DP protein has been isolated and purified, and the nucleotide sequence has been determined. The DP encoding DNA has been cloned into expression vectors and these expression vectors, when introduced into recombinant host cells, cause the recombinant host cells to express a functional DP receptor protein. The novel DP protein, the DP-encoding DNA, the expression vectors and recombinant host cells expressing recombinant DP are useful in the identification of modulators of DP receptor activity.
A method of identifying DP receptor modulators is also disclosed which utilizes the recombinant DP expressing host cells.
Modulators of DP activity are useful for the treatment of prostaglandin-related diseases and for modulating the effects of prostaglandins on the DP receptor.